Abstract: Vaccine strategies to treat central nervous system (CNS) cancers hold great promise. However, the mechanisms leading to generation of an immune response to CNS cancers are unclear. Specifically, the antigen presenting cell (APC) required to activate a CNS tumor antigen-specific T cell response is unknown. This is important both for rational vaccine development and for the incorporation of immunotherapies that may not be able to cross the blood-brain barrier, such as checkpoint blockade antibodies. To address this question, we generated a novel cell-type specific deletion of the H-2Kb MHC I molecule in C57BL/6 mice. By deleting Kb on proposed APCs, including dendritic cells (DCs) and microglia, we can define which APCs are required to result in effective vaccination for the murine GL261 glioma model using Theiler's murine encephalomyelitis virus (TMEV) as our vaccine platform. Our central hypothesis is that MHC class I expressed by DCs and microglia contribute to glioma- specific CD8 T cell responses in the CNS following tumor antigen-specific viral vaccination in vivo. Specifically, we will use a combination of our transgenic Kb conditional knockout animals and bone marrow transplantation models to determine the impact of specific compartments and specific cell types in generating immune responses against GL261 gliomas. We have demonstrated normal CD8 T cell development in dendritic cell-specific and macrophage-specific Kb conditional knockout animals. We have also demonstrated that macrophage-expressed Kb is not required to generate CD8 T cell responses in the CNS, either to an acute viral infection or following glioma vaccination. Therefore, we propose to assess the impact of Kb deletion on dendritic cells using a CD11c-cre Kb cKO strain and on microglia using a CX3CR1-creER Kb cKO strain on the immune response to a novel endogenous glioma antigen, tyrosinase-related protein 2 (TRP-2). We will assess immune cell infiltration using flow cytometry, and will assess tumor burden with bioluminescence imaging and small animal magnetic resonance imaging (MRI). Additionally, by using bone marrow transplantation, we will confirm the origin of the cell types required to generate glioma antigen-specific immune responses. Our lab is equipped with unique tools to address the impact of antigen presentation by multiple different cell types to address a critical gap in knowledge for glioma immunotherapies.